Buggy code:
public class ColumnFamilyStore implements ColumnFamilyStoreMBean { private static Logger logger_ = LoggerFactory . getLogger ( ColumnFamilyStore . class ) ; private static ExecutorService flushSorter_ = new JMXEnabledThreadPoolExecutor ( 1 , Runtime . getRuntime ( ) . availableProcessors ( ) , StageManager . KEEPALIVE , TimeUnit . SECONDS , new LinkedBlockingQueue < Runnable > ( Runtime . getRuntime ( ) . availableProcessors ( ) ) , new NamedThreadFactory ( "FLUSH-SORTER-POOL" ) ) ; private static ExecutorService flushWriter_ = new JMXEnabledThreadPoolExecutor ( 1 , DatabaseDescriptor . getFlushWriters ( ) , StageManager . KEEPALIVE , TimeUnit . SECONDS , new LinkedBlockingQueue < Runnable > ( DatabaseDescriptor . getFlushWriters ( ) ) , new NamedThreadFactory ( "FLUSH-WRITER-POOL" ) ) ; private static ExecutorService commitLogUpdater_ = new JMXEnabledThreadPoolExecutor ( "MEMTABLE-POST-FLUSHER" ) ; private Set < Memtable > memtablesPendingFlush = new ConcurrentSkipListSet < Memtable > ( ) ; private final String table_ ; public final String columnFamily_ ; private volatile Integer memtableSwitchCount = 0 ; private AtomicInteger fileIndexGenerator_ = new AtomicInteger ( 0 ) ; private Memtable memtable_ ; private AtomicReference < BinaryMemtable > binaryMemtable_ ; private SSTableTracker ssTables_ ; private LatencyTracker readStats_ = new LatencyTracker ( ) ; private LatencyTracker writeStats_ = new LatencyTracker ( ) ; private long minRowCompactedSize = 0L ; private long maxRowCompactedSize = 0L ; private long rowsCompactedTotalSize = 0L ; private long rowsCompactedCount = 0L ; ColumnFamilyStore ( String table , String columnFamilyName , int indexValue ) { } public void addToCompactedRowStats ( Long rowsize ) { } public long getMinRowCompactedSize ( ) { } public long getMaxRowCompactedSize ( ) { } public long getMeanRowCompactedSize ( ) { } public static ColumnFamilyStore createColumnFamilyStore ( String table , String columnFamily ) { } private Set < File > files ( ) { } public String getColumnFamilyName ( ) { } private static String getColumnFamilyFromFileName ( String filename ) { } public static int getGenerationFromFileName ( String filename ) { } public String getFlushPath ( ) { } public String getTempSSTablePath ( String directory ) { } Future < ? > maybeSwitchMemtable ( Memtable oldMemtable , final boolean writeCommitLog ) { flusherLock . writeLock ( ) . lock ( ) ; try { if ( oldMemtable . isFrozen ( ) ) { return null ; } oldMemtable . freeze ( ) ; final CommitLogSegment . CommitLogContext ctx = ( writeCommitLog ) ? CommitLog . instance ( ) . getContext ( ) : null ; ColumnFamilyStore . logger_ . info ( ( ( ( columnFamily_ ) + "<seq2seq4repair_space>has<seq2seq4repair_space>reached<seq2seq4repair_space>its<seq2seq4repair_space>threshold;<seq2seq4repair_space>switching<seq2seq4repair_space>in<seq2seq4repair_space>a<seq2seq4repair_space>fresh<seq2seq4repair_space>Memtable<seq2seq4repair_space>at<seq2seq4repair_space>" ) + ctx ) ) ; final Condition condition = submitFlush ( oldMemtable ) ; memtable_ = new Memtable ( this ) ; return ColumnFamilyStore . commitLogUpdater_ . submit ( new WrappedRunnable ( ) { public void runMayThrow ( ) throws IOException , InterruptedException { condition . await ( ) ; if ( writeCommitLog ) { final int cfId = DatabaseDescriptor . getTableMetaData ( table_ ) . get ( columnFamily_ ) . cfId ; <START_BUG> ColumnFamilyStore . logger_ . info ( ( "Discarding<seq2seq4repair_space>" + cfId ) ) ; <END_BUG> CommitLog . instance ( ) . discardCompletedSegments ( cfId , ctx ) ; } } } ) ; } finally { flusherLock . writeLock ( ) . unlock ( ) ; if ( ( memtableSwitchCount ) == ( Integer . MAX_VALUE ) ) { memtableSwitchCount = 0 ; } ( memtableSwitchCount ) ++ ; } } void switchBinaryMemtable ( DecoratedKey key , byte [ ] buffer ) { } public void forceFlushIfExpired ( ) { } public Future < ? > forceFlush ( ) { } public void forceBlockingFlush ( ) throws InterruptedException , ExecutionException { } public void forceFlushBinary ( ) { } Memtable apply ( DecoratedKey key , ColumnFamily columnFamily ) { } void applyBinary ( DecoratedKey key , byte [ ] buffer ) { } public static ColumnFamily removeDeleted ( ColumnFamily cf , int gcBefore ) { } private static void removeDeletedStandard ( ColumnFamily cf , int gcBefore ) { } private static void removeDeletedSuper ( ColumnFamily cf , int gcBefore ) { } public void addSSTable ( SSTableReader sstable ) { } long getExpectedCompactedFileSize ( Iterable < SSTableReader > sstables ) { } SSTableReader getMaxSizeFile ( Iterable < SSTableReader > sstables ) { } void forceCleanup ( ) { } public Table getTable ( ) { } void markCompacted ( Collection < SSTableReader > sstables ) { } boolean isCompleteSSTables ( Collection < SSTableReader > sstables ) { } void replaceCompactedSSTables ( Collection < SSTableReader > sstables , Iterable < SSTableReader > replacements ) { } Condition submitFlush ( IFlushable flushable ) { } public int getMemtableColumnsCount ( ) { } public int getMemtableDataSize ( ) { } public int getMemtableSwitchCount ( ) { } private Memtable getMemtableThreadSafe ( ) { } public Collection < SSTableReader > getSSTables ( ) { } public long getReadCount ( ) { } public double getRecentReadLatencyMicros ( ) { } public long [ ] getLifetimeReadLatencyHistogramMicros ( ) { } public long [ ] getRecentReadLatencyHistogramMicros ( ) { } public long getTotalReadLatencyMicros ( ) { } public int getPendingTasks ( ) { } public long getWriteCount ( ) { } public long getTotalWriteLatencyMicros ( ) { } public double getRecentWriteLatencyMicros ( ) { } public long [ ] getLifetimeWriteLatencyHistogramMicros ( ) { } public long [ ] getRecentWriteLatencyHistogramMicros ( ) { } public ColumnFamily getColumnFamily ( DecoratedKey key , QueryPath path , byte [ ] start , byte [ ] finish , List < byte [ ] > bitmasks , boolean reversed , int limit ) { } public ColumnFamily getColumnFamily ( DecoratedKey key , QueryPath path , byte [ ] start , byte [ ] finish , boolean reversed , int limit ) { } public ColumnFamily getColumnFamily ( QueryFilter filter ) { } private ColumnFamily cacheRow ( DecoratedKey key ) { } public ColumnFamily getColumnFamily ( QueryFilter filter , int gcBefore ) { } private ColumnFamily getTopLevelColumns ( QueryFilter filter , int gcBefore ) { }

Fix:
ColumnFamilyStore . logger_ . debug ( "Discarding<seq2seq4repair_space>{}" , cfId ) ;